A great number of biochemical determination reactions are based on biospecific affinity reactions between a receptor and a ligand. As examples of such reactions can be mentioned immunochemical reactions between an antigen and an antibody, enzymatic determination methods such as enzyme-substrate or enzyme-coenzyme, lektin-sugar, etc. Usually the ligand is the component to be determined. It is dissolved in a liquid, whereas the receptor is immobilized on a carrier in contact with the liquid. By letting a known amount of the ligand, which is labelled with an indicatable group, a so-called marker, compete with the unlabelled ligand one can determine the amount of unlabelled ligand which is present in a sample. Alternatively the measurement can be performed by adding an excess of the labelled ligand after the reaction with the unlabelled ligand.
In for example Radio Immuno Assay, so-called RIA technique, radioactive isotopes are used as markers. In this technique e.g. antigen molecules are allowed to compete in a sample with added isotope-labelled antigen molecules for the available sites on antibodies which are bonded to the carrier. After the reaction non-bonded material is removed by washing, the amount of residual activity on the carrier being an indication of the antigen concentration in the sample. As mentioned above one can, as an alternative, add the antigen sample to the carrier before the addition of the isotope-labelled antigen. An alternative determination method is Enzyme Immuno Assay (so-called EIA technique), wherein chromogenic or fluorgenic markers are used instead of radioactive markers, but for the rest the EIA technique is analogous with the RIA technique.
In these and similar biospecific determination methods in heterogeneous systems various types of material of varying physical forms have been used as carriers or solid phase. Examples of carriers which have been used are small balls of gel-forming materials such as cross-linked polysaccharides, polyacrylamide and the like or of cellulose, small paper discs, the inner surface of test tubes, etc. It has also been suggested to use matrix bodies with open pores ("sponges") having such a pore size that they absorb the liquid phase and retain the same so that the reaction proceeds within the solid phase.
The porous matrixes have several advantages compared to other matrix materials, not the least in that the reaction speed can be optimized because of the large surface area for the reaction. A drawback of the prior art systems using porous matrixes--and of most other solid matrixes--has been the difficulties to handle the matrixes in a simple manner during the various steps of the analysis, especially the handling between reaction steps, washing steps and measurement.
In the published Swedish patent application No. 7305361-3 there is disclosed a porous matrix and its use for determining the contents of a special enzyme in a serum sample. The disclosed matrix is formed as an elastically compressible sponge of synfthetic material, e.g. polyurethane, and it is covered with a layer of hormone-binding proteins and antibodies such as insuline antibodies. The porous sponge is placed in a reaction tube which on top of the sponge has a manually actuable piston which seals against the tube wall and is designed to compress the sponge to make the same free from occluded air. The bottom of the reaction tube is provided with a comparatively small nozzle which can be closed. The reaction liquid is sucked into the sponge by compressing the same manually, while the bottom channel is open, by means of the piston The piston is then withdrawn, thereby causing sample solution and radioactive reaction solution to be sucked into the sponge. After the absorption of liquid the bottom nozzle is closed and incubation is performed for several hours, whereupon the absorbed liquid is squeezed out by means of the piston and the radioactivity of the sponge or of the expelled liquid is measured. As an alternative the sample may be absorbed and incubated first, the reaction solution being absorbed and incubated in a separate step after the sample solution has been expelled by means of the piston. This known analysis device is thus handled entirely manually by actuation of the piston, and the problems involved in intermediate washing steps are not at all mentioned. Furthermore, the suction procedure is complicated since it requires both manual compression of the piston and withdrawal of the same for creating the necessary suction force. In summary the device according to the published Swedish patent application No. 7305361-3 involves a complex procedure which is not suitable for automation, and the liquid-retaining properties of the matrix are not used at all.
SE-A-7507846-9 (423 457) discloses a system for washing ball-shaped bodies, which can be used for immunoassays. These balls are not porous and cannot be compressed.